Dockerized service exposing a REST interface for rendering draw.io diagrams into images.
Diagrams.net has added command-line options to Draw.io Desktop which allow you to automate converting diagrams into images. This is great!
Unfortunately, Draw.io Desktop is an Electron-based application, and cannot execute without first installing a huge number of dependencies, including a GUI environment such as X11 within which it can run. This makes it difficult to integrate into other services such as Jenkins build pipelines.
This package puts Draw.io Desktop into a Docker container along with all of its dependencies and a simple HTTP REST server, allowing you to easily call it from other services regardless of platform or language.
Due to the large number of dependencies, the container produced is very big; I welcome contributions to trim its size down! In the meantime, at least all of this bloat is hidden inside this one container and won't affect the rest of your services.
docker run -d -p 5000:5000 --shm-size=1g tomkludy/drawio-renderer:latest
Note the --shm-size parameter; this determines the maximum memory that can be used during diagram rendering. If omitted, the default is 256mb. If you hit out-of-memory errors (HTTP status code 413), try increasing the value of this parameter.
New in v1.1: Now it is simpler to use the service from the command-line using curl, wget, Invoke-WebRequest or similar. Specify the Accept: request header to the desired output type and send the draw.io file as request content to the /convert_file endpoint; for example:
curl -d @inputfile.drawio -H "Accept: application/pdf" http://localhost:5000/convert_file?crop=true --output outputfile.pdf
Supported Accept: values:
| MIME type | Image format |
|---|---|
image/png |
PNG |
image/jpeg |
JPEG |
application/pdf |
|
image/svg+xml; encoding=utf-8 |
SVG |
Supported query parameters:
| Parameter | Description |
|---|---|
quality={n} |
Output image quality for JPEG (1-100, default: 90) |
transparent=true |
Use transparent background for PNG |
embed=true |
Includes a copy of the diagram (for PNG format only) |
border={n} |
Sets the border width around the diagram (0-10000, default: 0) |
scale={n.m} |
Scales the diagram size (0.0-5.0, 1.0 is default size |
width={n} |
Fits the generated image/pdf into the specified width, preserves aspect ratio (10-131072) |
height={n} |
Fits the generated image/pdf into the specified height, preserves aspect ratio (10-131072) |
crop=true |
Crops PDF to diagram size |
For full API documentation, start up the container and navigate to the /docs route with your browser; for example: http://localhost:5000/docs
This would not have been possible without this post from Joel Martin; he resolved most of the hard issues.
Note: contrary to the linked comment thread, this approach does NOT require --cap-add SYS_ADMIN.